Page 191 - Visions of the Future Chemistry and Life Science

172 V. WALSH

These discoveries ushered in the first wave of stimulation studies as a
means of reverse engineering brain function. Physiologists began to apply
electrical stimulation to the cerebral cortex (the outer surface of the brain),
and in doing so were able to produce movements in muscles on the contra-
lateral side of the body (the movements of one side of you body are con-
trolled by the opposite side of your brain, so magnetic or electrical
stimulation of, say, the left half of your brain will cause movements on the
right side of your body). Working on dogs and monkeys, David Ferrier used
magnetically induced currents to produce a map of cortical function
(Figure 10.1) and the technique of direct stimulation to map function was
later extended to human subjects. Progress in brain stimulation was rapid
and reached its first peak when Wilder Penfield and his colleagues applied
electrical stimulation to the cortex of patients undergoing neurosurgery
and were able to work out the way in which body movements were repre-
sented in the brain (Figure 10.2). They also confirmed the location of
speech reception and production areas, identified a third speech-related
area and stimulated areas that produced specifically tactile or visual sen-
sations. One patient, identified as Case J.V. (patients are usually referred to
by their initials for confidentiality), experienced seeing familiar people and
familiar scenes when stimulated in the temporal lobe.
There were several limitations to these methods of investigating brain
function. The invasive nature of the experiments meant that they could
only be carried out in patients who were awaiting surgery and of course this
restricts the kinds of experiments one can do. Another important limit was
the specificity of the movements or perceptions produced. The motor
cortex is required for fine control and important skills such as giving
complex hand signals to other road-users, but Penfield’s stimulation elic-
ited actions which were ‘not more complicated than those a newborn
infant is able to perform’. Some brain regions, however, which Penfield and
Rasmussen referred to as ‘elaboration areas’ apparently did not respond to
electrical stimulation because the brain does not only produce perceptual
and motor outputs but also transforms them: it would be difficult to
imagine how stimulation would elicit awareness of a transformation. For
example, at some stage in reading, your brain is able to translate printed
letters into sounds but stimulation never caused a subject to report any-
thing like this. Reading probably seems so automatic that you may even
have difficulty imagining that a written word is translated into a sound.
The closest you might get is to read something like ‘the door slammed